The invention relates to a circular or endless loop of the type comprising a core in the form of a plurality of yarn skeins and a seamless, woven protective sheath which encloses the entire core with considerable play. A loop of this type is disclosed in German Application DE-B 2,129,837.
It is significant for such loops that the core fills the cross sectional area of the protective sheath only to about 50 to 70 percent so that such loops are thus freely movable relative to the protective sheath and that the individual turns of the core are likewise not fixed relative to the protective sheath and to one another. Only in this way is it possible for the different turns to move relative to one another under load and to assume the same length due to the load so that overloading of an individual thread turn is avoided.
One feature of such a loop is also that in the unstressed state the protective sheath is somewhat longer than the core so that the protective sheath is lightly folded along the core.
The manufacturing process for such a loop is described in greater detail in German Application DE-B 2,129,837.
For this purpose, the prefabricated protective sheath is pushed longitudinally over a tube which is continuously open over a circumferential region of about 180.degree., i.e. has the shape of a trough; the sheath is thus pushed together longitudinally or upset, respectively, to less than half its length so that the sheath encloses the tube in an extensively folded manner. Then a thread of a textile yarn, of plastic or the like is pulled longitudinally through the interior of the tube or through the interior of the protective sheath, respectively. The pulled-through end of the yarn is then returned along the outside of the protective sheath to the insertion end and is again pulled longitudinally through the protective sheath or through the trough, respectively. This process is repeated many times in such a manner that a yarn skein is formed which comprises many circular layers of but a single thread. Due to the large number of juxtaposed layers of yarn which pass through the protective sheath, it is not necessary to knot or connect the ends of the yarn together. Rather, the ends may remain loose without thus adversely affecting the tensile strength of the yarn skein. After producing the yarn skein in such a manner, the protective sheath is pushed away from the trough in the longitudinal direction toward the yarn skein or skeins. The yarn skein is then removed from the trough so that it also is free. Then the upset protective sheath is pushed over the entire circumference of the yarn skein. Its ends are pushed together and preferably sewn to each other. The protective sheath has such an initial length that in its final state it is still somewhat longer than the yarn skein or skeins which it encloses. Thus it encloses the yarn skein or skeins with a slight amount of folding.
A significant feature of such known loops is that in their regions where they contact the crane hook or the load they have a very flat-oval cross-sectional configuration in which the individual threads of the yarn skein or skeins lie essentially next to one another and not on top of one another. This fact in particular takes care of uniform load distribution to the individual turns of the yarn skein.